Brady testified during Weis' medical malpractice lawsuit against two Massachusetts General surgeons.
"At that moment I wasn't sure what was happening, if that was normal or not normal," Brady said in Suffolk Superior Court. "As it developed, I realized this was a very serious issue we were dealing with."
Weis, the Patriots former offensive coordinator, claims in the lawsuit that physicians Charles Ferguson and Richard Hodin acted negligently by failing to recognize life-threatening internal bleeding and infection after the June 2002 surgery. He was in the hospital for more than a month and claims he still suffers from nerve damage in his feet.
Weis is seeking unspecified damages.
His attorneys rested their case later Friday. Ferguson and Hodin have denied any wrongdoing.
Ferguson testified Friday that he performed the surgery, and routine post-operative tests showed no problems.
"Weis had a little more incisional pain than normal," he said. "He was breathing easy, his pulse was fine and his urine output was fine."
That was on a Friday. Ferguson left for the weekend, leaving Hodin in charge of his patients. When he returned Monday morning he said Weis was "critically ill."
Ferguson also told the court Weis insisted on accelerating the pre-op program, so he could be ready for the Patriots' summer camp. Weis had the surgery within two weeks of his first consultation.
"I was concerned he did not go through the normal six-week training session to teach you how to eat and what to eat after the operation," the doctor said.
Ferguson said after explaining the process, Weis had no follow-up questions.
"He told me he had done the research on this, and he didn't have any questions," Ferguson said.
Ferguson also countered claims by Dr. Alan Wittgrove, an expert witness called by Weis' lawyers on Thursday.
Wittgrove said Weis continued to get a blood-thinning drug even after internal bleeding was detected, and blamed nerve damage on a lack of thiamin, a vitamin.
But Ferguson said Friday the blood thinner was administered at low doses to prevent a pulmonary embolism and that Weis was getting thiamin through his intravenous feeding tubes.
Weis testified earlier in the week that Brady was the only member of the Patriots, beside the team doctor, he told about the surgery. Brady testified about the special relationship he had with Weis.
"He's always been an extremely intense person, intense coach. ... He expects the best out of everybody and teaches you to be accountable and to be responsible, and that's kind of what I fed off," Brady said.
During the cross-examination, Brady said Weis' personality didn't change after the surgery.